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From: moore@cs.washington.edu (Charles Moore)
Newsgroups: comp.sys.mac.hypercard
Subject: Is PasToZero necessary?
Keywords: XCMD's, PasToZero
Message-ID: <12477@june.cs.washington.edu>
Date: 6 Jul 90 08:05:58 GMT
Organization: U of Washington, Computer Science, Seattle
Lines: 22

Is a call to PasToZero necessary in order to return a result to Hypercard
from an XCMD?  The appendix to the HyperCard Script Language Guide is
pretty cagey about this saying only that the returnValue field of the
XCmdBlock can contain a handle to a zero-terminated string.  But where
is the space for this string allocated?  I allocated space within my
XCMD with the declaration:

char resultStr[80];

and then tried to return this value with the assignment:

paramPtr->returnValue = (Handle)&resultStr;

The result was a system error.  Does this mean that PasToZero, in 
addition to converting between string types, also commands HyperCard
to allocate space for the converted string?  If so, why must I use
PasToZero?  I already have a zero-terminated string.  I don't need to
convert it; I just need to return it.  Where is the glue routine that
has HyperCard allocate some space and copies your string into that 
space but that doesn't waste time doing unnecessary conversions?

Charles Moore